Royal commentator Camilla Tominey has told Daybreak that Kate's severe morning sickness has forced the royal couple to announce her pregnancy early.
She said: "They would not have wanted to release this information before 12 weeks but they couldn't have kept a hospital visit under-wraps."
The Duchess of Cambridge left hospital today, after three days of treatment for a severe form of morning sickness.
A nurse disclosed information about Kate's condition to two DJs who rang the hospital claiming to be the Queen and Prince Charles.
The Duchess of Cambridge is to spend another night in hospital being treated for acute morning sickness but is said to be feeling better.